Accurate testing of splined parts under simulated conditions to determine such factors as wear and fatigue life is simplified by the use of four-square torque machines. Such machines are adapted to have dialed into them a predetermined torque for simulating load even though the machines and test specimens are at rest. Only minimal power is then required to rotate the specimen at designed speeds. This alleviates the need to actually transmit through the test specimen the total power to which it is designed and then have to absorb that power by means such as a pony brake on the output side.
Four-square test machines have long been known in the art for torque-testing power transmitting machine elements. This type of test machine normally involves a first pair of shafts rotatable connected to each other and interconnected with a second pair of like shafts in a manner permitting the locking-in of a torque to create artificial or simulated loads. The principle of this type of machine is disclosed in U.S. Pat. No. 3,078,711, wherein gears and shafts are formed in a loop to define a four-square into which static torque is applied. The contribution made by the disclosure of this patent is that the machine at rest is under no load, and torque is applied progressively as rotational speed increases to simulate actual drive conditions. U.S. Pat. No. 3,112,643 provides a four-square test machine having capability of providing torsional input to the loop while the machine is rotated. The idea of providing apparatus for varying the locked-in torque is disclosed in U.S. Pat. No. 3,195,350. It is capable of applying torque loading in either direction such as would be experienced in driving certain types of machinery. It is known, such as in U.S. Pat. No. 3,796,092, to apply lateral forces to test specimen under simulated actual working conditions.